Simultaneous pancreas kidney transplantation (SPK) is an increasingly common treatment option for patients with end-stage renal disease due to Type I diabetes (DM). Recent studies suggest SPK may improve kidney allograft survival compared to kidney transplantation alone (KA). However, patient selection may account for this disparity since patient sociodemographics and comorbidities likely impact consideration for SPK. The objectives of this study are to assess the impact of patient selection on access to SPK versus KA and to determine the impact of SPK on renal allograft survival. In order to avoid selection bias, the comparison of renal allograft survival between SPK and KA recipients will be limited to patients waitlisted for SPK: approximately 10 percent of patients listed for SPK receive a KA due a fatty or traumatized pancreas allograft, or availability of a zero-antigen mismatch kidney alone. The USRDS has collected comorbidity data since April 1995. To assess the impact of patient selection on access to SPK we will use these national data to conduct a cross-sectional study of DM patients waitlisted for either SPK or KA after April 1995. We will compare patient socioeconomic demographics, comorbidities, and transplant center characteristics between these two groups. Logistic regression will be used to identify independent determinants of access to SPK. To determine the impact of SPK on renal allograft survival, we will conduct a retrospective cohort study of all patients waitlisted for SPK and transplanted with SPK or KA after April 1995. Renal allograft survival in SPK and KA will be compared using Cox proportional hazards models, adjusting for patient and transplant center characteristics.